Lemmy communities are glorified RSS feeds, you can even subscribe to them through RSS and not care whether your instance is down for maintenance to read the posts.
What I've said already: once the RSS client gets the feed, it's on your device. Meaning you can access the items off-line, filter and sort by whatever criteria you wish (and your client allows), delete them, mark to read later, etc.
You can create a feed that only includes Lemmy communities dedicated to a specific topic - like only those related to video games in some broad sense. Or a news-only feed.
It's much more convenient that just subscribing to everything you're interested in and then trying to filter out on our own (good luck not forgetting stuff), as you're basically on the algorithm's mercy as well.
Lemmy, too, has algorithms that determine what you see - how many upvotes a post has, how many comments, how recent, etc. The communities you subscribe to may have some high-quality, niche posts that you're very likely to miss because they're overshadowed by bigger, more active communities where posts simply gain more traction - RSS lets you circumvent that.
@drwho yep, that is correct. I also have feeds in all my readers that are displayed completely, while others are just back links to the article in question.